1 ====================================
2 Getting Started with the LLVM System
3 ====================================
11 Welcome to LLVM! In order to get started, you first need to know some basic
14 First, LLVM comes in three pieces. The first piece is the LLVM suite. This
15 contains all of the tools, libraries, and header files needed to use LLVM. It
16 contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
17 also contains basic regression tests that can be used to test the LLVM tools and
20 The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
21 component compiles C, C++, Objective C, and Objective C++ code into LLVM
22 bitcode. Once compiled into LLVM bitcode, a program can be manipulated with the
23 LLVM tools from the LLVM suite.
25 There is a third, optional piece called Test Suite. It is a suite of programs
26 with a testing harness that can be used to further test LLVM's functionality
29 Getting Started Quickly (A Summary)
30 ===================================
32 The LLVM Getting Started documentation may be out of date. So, the `Clang
33 Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
36 Here's the short story for getting up and running quickly with LLVM:
38 #. Read the documentation.
39 #. Read the documentation.
40 #. Remember that you were warned twice about reading the documentation.
42 * In particular, the *relative paths specified are important*.
46 * ``cd where-you-want-llvm-to-live``
47 * ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
51 * ``cd where-you-want-llvm-to-live``
53 * ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
55 #. Checkout Compiler-RT (required to build the sanitizers) **[Optional]**:
57 * ``cd where-you-want-llvm-to-live``
58 * ``cd llvm/projects``
59 * ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
61 #. Checkout Libomp (required for OpenMP support) **[Optional]**:
63 * ``cd where-you-want-llvm-to-live``
64 * ``cd llvm/projects``
65 * ``svn co http://llvm.org/svn/llvm-project/openmp/trunk openmp``
67 #. Checkout libcxx and libcxxabi **[Optional]**:
69 * ``cd where-you-want-llvm-to-live``
70 * ``cd llvm/projects``
71 * ``svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx``
72 * ``svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi``
74 #. Get the Test Suite Source Code **[Optional]**
76 * ``cd where-you-want-llvm-to-live``
77 * ``cd llvm/projects``
78 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
80 #. Configure and build LLVM and Clang:
82 *Warning:* Make sure you've checked out *all of* the source code
83 before trying to configure with cmake. cmake does not pickup newly
84 added source directories in incremental builds.
86 The build uses `CMake <CMake.html>`_. LLVM requires CMake 3.4.3 to build. It
87 is generally recommended to use a recent CMake, especially if you're
88 generating Ninja build files. This is because the CMake project is constantly
89 improving the quality of the generators, and the Ninja generator gets a lot
92 * ``cd where you want to build llvm``
95 * ``cmake -G <generator> [options] <path to llvm sources>``
97 Some common generators are:
99 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
100 * ``Ninja`` --- for generating `Ninja <https://ninja-build.org>`_
101 build files. Most llvm developers use Ninja.
102 * ``Visual Studio`` --- for generating Visual Studio projects and
104 * ``Xcode`` --- for generating Xcode projects.
108 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
109 pathname of where you want the LLVM tools and libraries to be installed
110 (default ``/usr/local``).
112 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
113 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
115 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
116 (default is Yes for Debug builds, No for all other build types).
118 * Run your build tool of choice!
120 * The default target (i.e. ``make``) will build all of LLVM
122 * The ``check-all`` target (i.e. ``make check-all``) will run the
123 regression tests to ensure everything is in working order.
125 * CMake will generate build targets for each tool and library, and most
126 LLVM sub-projects generate their own ``check-<project>`` target.
128 * Running a serial build will be *slow*. Make sure you run a
129 parallel build; for ``make``, use ``make -j``.
131 * For more information see `CMake <CMake.html>`_
133 * If you get an "internal compiler error (ICE)" or test failures, see
136 Consult the `Getting Started with LLVM`_ section for detailed information on
137 configuring and compiling LLVM. Go to `Directory Layout`_ to learn about the
138 layout of the source code tree.
143 Before you begin to use the LLVM system, review the requirements given below.
144 This may save you some trouble by knowing ahead of time what hardware and
145 software you will need.
150 LLVM is known to work on the following host platforms:
152 ================== ===================== =============
154 ================== ===================== =============
155 Linux x86\ :sup:`1` GCC, Clang
156 Linux amd64 GCC, Clang
157 Linux ARM\ :sup:`4` GCC, Clang
158 Linux PowerPC GCC, Clang
159 Solaris V9 (Ultrasparc) GCC
160 FreeBSD x86\ :sup:`1` GCC, Clang
161 FreeBSD amd64 GCC, Clang
162 MacOS X\ :sup:`2` PowerPC GCC
163 MacOS X x86 GCC, Clang
164 Cygwin/Win32 x86\ :sup:`1, 3` GCC
165 Windows x86\ :sup:`1` Visual Studio
166 Windows x64 x86-64 Visual Studio
167 ================== ===================== =============
171 #. Code generation supported for Pentium processors and up
172 #. Code generation supported for 32-bit ABI only
173 #. To use LLVM modules on Win32-based system, you may configure LLVM
174 with ``-DBUILD_SHARED_LIBS=On``.
175 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
177 Note that Debug builds require a lot of time and disk space. An LLVM-only build
178 will need about 1-3 GB of space. A full build of LLVM and Clang will need around
179 15-20 GB of disk space. The exact space requirements will vary by system. (It
180 is so large because of all the debugging information and the fact that the
181 libraries are statically linked into multiple tools).
183 If you you are space-constrained, you can build only selected tools or only
184 selected targets. The Release build requires considerably less space.
186 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
187 so. If compilation is successful, the LLVM utilities should be able to
188 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
189 should work as well, although the generated native code may not work on your
195 Compiling LLVM requires that you have several software packages installed. The
196 table below lists those required packages. The Package column is the usual name
197 for the software package that LLVM depends on. The Version column provides
198 "known to work" versions of the package. The Notes column describes how LLVM
199 uses the package and provides other details.
201 =========================================================== ============ ==========================================
202 Package Version Notes
203 =========================================================== ============ ==========================================
204 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
205 `GCC <http://gcc.gnu.org/>`_ >=4.8.0 C/C++ compiler\ :sup:`1`
206 `python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
207 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`3`
208 =========================================================== ============ ==========================================
212 #. Only the C and C++ languages are needed so there's no need to build the
213 other languages for LLVM's purposes. See `below` for specific version
215 #. Only needed if you want to run the automated test suite in the
216 ``llvm/test`` directory.
217 #. Optional, adds compression / uncompression capabilities to selected LLVM
220 Additionally, your compilation host is expected to have the usual plethora of
221 Unix utilities. Specifically:
223 * **ar** --- archive library builder
224 * **bzip2** --- bzip2 command for distribution generation
225 * **bunzip2** --- bunzip2 command for distribution checking
226 * **chmod** --- change permissions on a file
227 * **cat** --- output concatenation utility
228 * **cp** --- copy files
229 * **date** --- print the current date/time
230 * **echo** --- print to standard output
231 * **egrep** --- extended regular expression search utility
232 * **find** --- find files/dirs in a file system
233 * **grep** --- regular expression search utility
234 * **gzip** --- gzip command for distribution generation
235 * **gunzip** --- gunzip command for distribution checking
236 * **install** --- install directories/files
237 * **mkdir** --- create a directory
238 * **mv** --- move (rename) files
239 * **ranlib** --- symbol table builder for archive libraries
240 * **rm** --- remove (delete) files and directories
241 * **sed** --- stream editor for transforming output
242 * **sh** --- Bourne shell for make build scripts
243 * **tar** --- tape archive for distribution generation
244 * **test** --- test things in file system
245 * **unzip** --- unzip command for distribution checking
246 * **zip** --- zip command for distribution generation
251 Host C++ Toolchain, both Compiler and Standard Library
252 ------------------------------------------------------
254 LLVM is very demanding of the host C++ compiler, and as such tends to expose
255 bugs in the compiler. We are also planning to follow improvements and
256 developments in the C++ language and library reasonably closely. As such, we
257 require a modern host C++ toolchain, both compiler and standard library, in
260 For the most popular host toolchains we check for specific minimum versions in
267 Anything older than these toolchains *may* work, but will require forcing the
268 build system with a special option and is not really a supported host platform.
269 Also note that older versions of these compilers have often crashed or
272 For less widely used host toolchains such as ICC or xlC, be aware that a very
273 recent version may be required to support all of the C++ features used in LLVM.
275 We track certain versions of software that are *known* to fail when used as
276 part of the host toolchain. These even include linkers at times.
278 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
279 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
280 defined in a discarded section. You can safely ignore these messages as they are
281 erroneous and the linkage is correct. These messages disappear using ld 2.17.
283 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
284 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
285 times (minutes instead of seconds) when building LLVM. We recommend upgrading
286 to a newer version (2.17.50.0.4 or later).
288 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
289 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
290 intermittent failures when building LLVM with position independent code. The
291 symptom is an error about cyclic dependencies. We recommend upgrading to a
292 newer version of Gold.
294 Getting a Modern Host C++ Toolchain
295 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
297 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
298 have a sufficiently modern Xcode, or you will likely need to upgrade until you
299 do. Windows does not have a "system compiler", so you must install either Visual
300 Studio 2015 or a recent version of mingw64. FreeBSD 10.0 and newer have a modern
301 Clang as the system compiler.
303 However, some Linux distributions and some other or older BSDs sometimes have
304 extremely old versions of GCC. These steps attempt to help you upgrade you
305 compiler even on such a system. However, if at all possible, we encourage you
306 to use a recent version of a distribution with a modern system compiler that
307 meets these requirements. Note that it is tempting to to install a prior
308 version of Clang and libc++ to be the host compiler, however libc++ was not
309 well tested or set up to build on Linux until relatively recently. As
310 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
311 initial host in a bootstrap, and then using Clang (and potentially libc++).
313 The first step is to get a recent GCC toolchain installed. The most common
314 distribution on which users have struggled with the version requirements is
315 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
316 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
317 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
318 not all users can use PPAs and there are many other distributions, so it may be
319 necessary (or just useful, if you're here you *are* doing compiler development
320 after all) to build and install GCC from source. It is also quite easy to do
323 .. _toolchain testing PPA:
324 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
325 .. _ask ubuntu stack exchange:
326 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
328 Easy steps for installing GCC 4.8.2:
330 .. code-block:: console
332 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
333 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
334 % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
335 % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
336 % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
337 % tar -xvjf gcc-4.8.2.tar.bz2
339 % ./contrib/download_prerequisites
341 % mkdir gcc-4.8.2-build
343 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
347 For more details, check out the excellent `GCC wiki entry`_, where I got most
348 of this information from.
351 http://gcc.gnu.org/wiki/InstallingGCC
353 Once you have a GCC toolchain, configure your build of LLVM to use the new
354 toolchain for your host compiler and C++ standard library. Because the new
355 version of libstdc++ is not on the system library search path, you need to pass
356 extra linker flags so that it can be found at link time (``-L``) and at runtime
357 (``-rpath``). If you are using CMake, this invocation should produce working
360 .. code-block:: console
364 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
365 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
367 If you fail to set rpath, most LLVM binaries will fail on startup with a message
368 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
369 found``. This means you need to tweak the -rpath linker flag.
371 When you build Clang, you will need to give *it* access to modern C++11
372 standard library in order to use it as your new host in part of a bootstrap.
373 There are two easy ways to do this, either build (and install) libc++ along
374 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
375 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
376 Clang will look within its own prefix for libstdc++ and use it if found. You
377 can also add an explicit prefix for Clang to look in for a GCC toolchain with
378 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
379 link commands when using your just-built-Clang to bootstrap.
381 .. _Getting Started with LLVM:
383 Getting Started with LLVM
384 =========================
386 The remainder of this guide is meant to get you up and running with LLVM and to
387 give you some basic information about the LLVM environment.
389 The later sections of this guide describe the `general layout`_ of the LLVM
390 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
391 more information about LLVM or to get help via e-mail.
393 Terminology and Notation
394 ------------------------
396 Throughout this manual, the following names are used to denote paths specific to
397 the local system and working environment. *These are not environment variables
398 you need to set but just strings used in the rest of this document below*. In
399 any of the examples below, simply replace each of these names with the
400 appropriate pathname on your local system. All these paths are absolute:
404 This is the top level directory of the LLVM source tree.
408 This is the top level directory of the LLVM object tree (i.e. the tree where
409 object files and compiled programs will be placed. It can be the same as
412 Unpacking the LLVM Archives
413 ---------------------------
415 If you have the LLVM distribution, you will need to unpack it before you can
416 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
417 and the LLVM GCC front end compiled for your platform. There is an additional
418 test suite that is optional. Each file is a TAR archive that is compressed with
421 The files are as follows, with *x.y* marking the version number:
425 Source release for the LLVM libraries and tools.
427 ``llvm-test-x.y.tar.gz``
429 Source release for the LLVM test-suite.
433 Checkout LLVM from Subversion
434 -----------------------------
436 If you have access to our Subversion repository, you can get a fresh copy of the
437 entire source code. All you need to do is check it out from Subversion as
440 * ``cd where-you-want-llvm-to-live``
441 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
442 * Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
444 This will create an '``llvm``' directory in the current directory and fully
445 populate it with the LLVM source code, Makefiles, test directories, and local
446 copies of documentation files.
448 If you want to get a specific release (as opposed to the most recent revision),
449 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
450 following releases are located in the following subdirectories of the '``tags``'
453 * Release 3.4: **RELEASE_34/final**
454 * Release 3.3: **RELEASE_33/final**
455 * Release 3.2: **RELEASE_32/final**
456 * Release 3.1: **RELEASE_31/final**
457 * Release 3.0: **RELEASE_30/final**
458 * Release 2.9: **RELEASE_29/final**
459 * Release 2.8: **RELEASE_28**
460 * Release 2.7: **RELEASE_27**
461 * Release 2.6: **RELEASE_26**
462 * Release 2.5: **RELEASE_25**
463 * Release 2.4: **RELEASE_24**
464 * Release 2.3: **RELEASE_23**
465 * Release 2.2: **RELEASE_22**
466 * Release 2.1: **RELEASE_21**
467 * Release 2.0: **RELEASE_20**
468 * Release 1.9: **RELEASE_19**
469 * Release 1.8: **RELEASE_18**
470 * Release 1.7: **RELEASE_17**
471 * Release 1.6: **RELEASE_16**
472 * Release 1.5: **RELEASE_15**
473 * Release 1.4: **RELEASE_14**
474 * Release 1.3: **RELEASE_13**
475 * Release 1.2: **RELEASE_12**
476 * Release 1.1: **RELEASE_11**
477 * Release 1.0: **RELEASE_1**
479 If you would like to get the LLVM test suite (a separate package as of 1.4), you
480 get it from the Subversion repository:
482 .. code-block:: console
485 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
487 By placing it in the ``llvm/projects``, it will be automatically configured by
488 the LLVM cmake configuration.
493 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
494 automatically with each Subversion commit and contain all necessary git-svn
495 marks (so, you can recreate git-svn metadata locally). Note that right now
496 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
499 .. code-block:: console
501 % git clone http://llvm.org/git/llvm.git
503 If you want to check out clang too, run:
505 .. code-block:: console
508 % git clone http://llvm.org/git/clang.git
510 If you want to check out compiler-rt (required to build the sanitizers), run:
512 .. code-block:: console
515 % git clone http://llvm.org/git/compiler-rt.git
517 If you want to check out libomp (required for OpenMP support), run:
519 .. code-block:: console
522 % git clone http://llvm.org/git/openmp.git
524 If you want to check out libcxx and libcxxabi (optional), run:
526 .. code-block:: console
529 % git clone http://llvm.org/git/libcxx.git
530 % git clone http://llvm.org/git/libcxxabi.git
532 If you want to check out the Test Suite Source Code (optional), run:
534 .. code-block:: console
537 % git clone http://llvm.org/git/test-suite.git
539 Since the upstream repository is in Subversion, you should use ``git
540 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
541 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
542 master branch, run the following command:
544 .. code-block:: console
546 % git config branch.master.rebase true
548 Sending patches with Git
549 ^^^^^^^^^^^^^^^^^^^^^^^^
551 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
553 Assume ``master`` points the upstream and ``mybranch`` points your working
554 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
555 sanity of whitespaces:
557 .. code-block:: console
559 % git diff --check master..mybranch
561 The easiest way to generate a patch is as below:
563 .. code-block:: console
565 % git diff master..mybranch > /path/to/mybranch.diff
567 It is a little different from svn-generated diff. git-diff-generated diff has
568 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
569 could be accepted with ``patch -p1 -N``.
571 But you may generate patchset with git-format-patch. It generates by-each-commit
572 patchset. To generate patch files to attach to your article:
574 .. code-block:: console
576 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
578 If you would like to send patches directly, you may use git-send-email or
579 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
581 .. code-block:: console
583 % git format-patch --attach master..mybranch --stdout | git imap-send
585 Then, your .git/config should have [imap] sections.
590 host = imaps://imap.gmail.com
591 user = your.gmail.account@gmail.com
596 folder = "[Gmail]/Drafts"
597 ; example for Japanese, "Modified UTF-7" encoded.
598 folder = "[Gmail]/&Tgtm+DBN-"
599 ; example for Traditional Chinese
600 folder = "[Gmail]/&g0l6Pw-"
602 .. _developers-work-with-git-svn:
604 For developers to work with git-svn
605 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
607 To set up clone from which you can submit code using ``git-svn``, run:
609 .. code-block:: console
611 % git clone http://llvm.org/git/llvm.git
613 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
614 % git config svn-remote.svn.fetch :refs/remotes/origin/master
615 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
617 # If you have clang too:
619 % git clone http://llvm.org/git/clang.git
621 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
622 % git config svn-remote.svn.fetch :refs/remotes/origin/master
625 Likewise for compiler-rt, libomp and test-suite.
627 To update this clone without generating git-svn tags that conflict with the
628 upstream Git repo, run:
630 .. code-block:: console
632 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
633 % git checkout master
636 git checkout master &&
639 Likewise for compiler-rt, libomp and test-suite.
641 This leaves your working directories on their master branches, so you'll need to
642 ``checkout`` each working branch individually and ``rebase`` it on top of its
645 For those who wish to be able to update an llvm repo/revert patches easily using
646 git-svn, please look in the directory for the scripts ``git-svnup`` and
649 To perform the aforementioned update steps go into your source directory and
650 just type ``git-svnup`` or ``git svnup`` and everything will just work.
652 If one wishes to revert a commit with git-svn, but do not want the git hash to
653 escape into the commit message, one can use the script ``git-svnrevert`` or
654 ``git svnrevert`` which will take in the git hash for the commit you want to
655 revert, look up the appropriate svn revision, and output a message where all
656 references to the git hash have been replaced with the svn revision.
658 To commit back changes via git-svn, use ``git svn dcommit``:
660 .. code-block:: console
664 Note that git-svn will create one SVN commit for each Git commit you have pending,
665 so squash and edit each commit before executing ``dcommit`` to make sure they all
666 conform to the coding standards and the developers' policy.
668 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
669 please make sure your current branch is up-to-date (via fetch/rebase) before
672 The git-svn metadata can get out of sync after you mess around with branches and
673 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
674 about files with uncommitted changes. The fix is to rebuild the metadata:
676 .. code-block:: console
681 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
683 For developers to work with a git monorepo
684 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
688 This set-up is using unofficial mirror hosted on GitHub, use with caution.
690 To set up a clone of all the llvm projects using a unified repository:
692 .. code-block:: console
694 % export TOP_LEVEL_DIR=`pwd`
695 % git clone https://github.com/llvm-project/llvm-project/
697 % git config branch.master.rebase true
699 You can configure various build directory from this clone, starting with a build
702 .. code-block:: console
705 % mkdir llvm-build && cd llvm-build
706 % cmake -GNinja ../llvm-project/llvm
710 .. code-block:: console
713 % mkdir lldb-build && cd lldb-build
714 % cmake -GNinja ../llvm-project/llvm -DLLVM_ENABLE_PROJECTS=lldb
716 Or a combination of multiple projects:
718 .. code-block:: console
721 % mkdir clang-build && cd clang-build
722 % cmake -GNinja ../llvm-project/llvm -DLLVM_ENABLE_PROJECTS="clang;libcxx;compiler-rt"
724 A helper script is provided in `llvm/utils/git-svn/git-llvm`. After you add it
725 to your path, you can push committed changes upstream with `git llvm push`.
727 .. code-block:: console
729 % export PATH=$PATH:$TOP_LEVEL_DIR/llvm-project/llvm/utils/git-svn/
732 While this is using SVN under the hood, it does not require any interaction from
734 After a few minutes, `git pull` should get back the changes as they were
735 commited. Note that a current limitation is that `git` does not directly record
736 file rename, and thus it is propagated to SVN as a combination of delete-add
737 instead of a file rename.
739 Local LLVM Configuration
740 ------------------------
742 Once checked out from the Subversion repository, the LLVM suite source code must
743 be configured before being built. This process uses CMake.
744 Unlinke the normal ``configure`` script, CMake
745 generates the build files in whatever format you request as well as various
746 ``*.inc`` files, and ``llvm/include/Config/config.h``.
748 Variables are passed to ``cmake`` on the command line using the format
749 ``-D<variable name>=<value>``. The following variables are some common options
750 used by people developing LLVM.
752 +-------------------------+----------------------------------------------------+
753 | Variable | Purpose |
754 +=========================+====================================================+
755 | CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
756 | | default, this will be /usr/bin/cc. |
757 +-------------------------+----------------------------------------------------+
758 | CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
759 | | default, this will be /usr/bin/c++. |
760 +-------------------------+----------------------------------------------------+
761 | CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
762 | | to generate files for. Valid options are Debug, |
763 | | Release, RelWithDebInfo, and MinSizeRel. Default |
765 +-------------------------+----------------------------------------------------+
766 | CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
767 | | running the install action of the build files. |
768 +-------------------------+----------------------------------------------------+
769 | LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
770 | | targets will be built and linked into llc. This is |
771 | | equivalent to the ``--enable-targets`` option in |
772 | | the configure script. The default list is defined |
773 | | as ``LLVM_ALL_TARGETS``, and can be set to include |
774 | | out-of-tree targets. The default value includes: |
775 | | ``AArch64, AMDGPU, ARM, BPF, Hexagon, Mips, |
776 | | MSP430, NVPTX, PowerPC, Sparc, SystemZ, X86, |
778 +-------------------------+----------------------------------------------------+
779 | LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
780 | | code This is disabled by default because it is |
781 | | slow and generates a lot of output. |
782 +-------------------------+----------------------------------------------------+
783 | LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
784 | | code. This is disabled by default because it is |
785 | | slow and generates a lot of output. |
786 +-------------------------+----------------------------------------------------+
787 | LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
788 | | default set of LLVM components that can be |
789 | | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
790 | | default contains most of LLVM and is defined in |
791 | | ``tools/llvm-shlib/CMakelists.txt``. |
792 +-------------------------+----------------------------------------------------+
793 | LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
794 | | the LLVM build. This can dramatically speed up |
796 +-------------------------+----------------------------------------------------+
798 To configure LLVM, follow these steps:
800 #. Change directory into the object root directory:
802 .. code-block:: console
806 #. Run the ``cmake``:
808 .. code-block:: console
810 % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
811 [other options] SRC_ROOT
813 Compiling the LLVM Suite Source Code
814 ------------------------------------
816 Unlike with autotools, with CMake your build type is defined at configuration.
817 If you want to change your build type, you can re-run cmake with the following
820 .. code-block:: console
822 % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
824 Between runs, CMake preserves the values set for all options. CMake has the
825 following build types defined:
829 These builds are the default. The build system will compile the tools and
830 libraries unoptimized, with debugging information, and asserts enabled.
834 For these builds, the build system will compile the tools and libraries
835 with optimizations enabled and not generate debug info. CMakes default
836 optimization level is -O3. This can be configured by setting the
837 ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
841 These builds are useful when debugging. They generate optimized binaries with
842 debug information. CMakes default optimization level is -O2. This can be
843 configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
846 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
847 directory and issuing the following command:
849 .. code-block:: console
853 If the build fails, please `check here`_ to see if you are using a version of
854 GCC that is known not to compile LLVM.
856 If you have multiple processors in your machine, you may wish to use some of the
857 parallel build options provided by GNU Make. For example, you could use the
860 .. code-block:: console
864 There are several special targets which are useful when working with the LLVM
869 Removes all files generated by the build. This includes object files,
870 generated C/C++ files, libraries, and executables.
874 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
875 under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
876 defaults to ``/usr/local``.
878 ``make docs-llvm-html``
880 If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
881 at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
886 It is possible to cross-compile LLVM itself. That is, you can create LLVM
887 executables and libraries to be hosted on a platform different from the platform
888 where they are built (a Canadian Cross build). To generate build files for
889 cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
890 define compiler flags and variables used during the CMake test operations.
892 The result of such a build is executables that are not runnable on on the build
893 host but can be executed on the target. As an example the following CMake
894 invocation can generate build files targeting iOS. This will work on Mac OS X
895 with the latest Xcode:
897 .. code-block:: console
899 % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES="armv7;armv7s;arm64"
900 -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
901 -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
902 -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
905 Note: There are some additional flags that need to be passed when building for
906 iOS due to limitations in the iOS SDK.
908 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
909 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
910 about cross-compiling.
912 The Location of LLVM Object Files
913 ---------------------------------
915 The LLVM build system is capable of sharing a single LLVM source tree among
916 several LLVM builds. Hence, it is possible to build LLVM for several different
917 platforms or configurations using the same source tree.
919 * Change directory to where the LLVM object files should live:
921 .. code-block:: console
927 .. code-block:: console
929 % cmake -G "Unix Makefiles" SRC_ROOT
931 The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
932 LLVM source tree. At each level where source files are present in the source
933 tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
934 Underneath that directory there is another directory with a name ending in
935 ``.dir`` under which you'll find object files for each source.
939 .. code-block:: console
942 % find lib/Support/ -name APFloat*
943 lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
945 Optional Configuration Items
946 ----------------------------
948 If you're running on a Linux system that supports the `binfmt_misc
949 <http://en.wikipedia.org/wiki/binfmt_misc>`_
950 module, and you have root access on the system, you can set your system up to
951 execute LLVM bitcode files directly. To do this, use commands like this (the
952 first command may not be required if you are already using the module):
954 .. code-block:: console
956 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
957 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
958 % chmod u+x hello.bc (if needed)
961 This allows you to execute LLVM bitcode files directly. On Debian, you can also
962 use this command instead of the 'echo' command above:
964 .. code-block:: console
966 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
974 One useful source of information about the LLVM source base is the LLVM `doxygen
975 <http://www.doxygen.org/>`_ documentation available at
976 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
982 Simple examples using the LLVM IR and JIT.
987 Public header files exported from the LLVM library. The three main subdirectories:
989 ``llvm/include/llvm``
991 All LLVM-specific header files, and subdirectories for different portions of
992 LLVM: ``Analysis``, ``CodeGen``, ``Target``, ``Transforms``, etc...
994 ``llvm/include/llvm/Support``
996 Generic support libraries provided with LLVM but not necessarily specific to
997 LLVM. For example, some C++ STL utilities and a Command Line option processing
998 library store header files here.
1000 ``llvm/include/llvm/Config``
1002 Header files configured by the ``configure`` script.
1003 They wrap "standard" UNIX and C header files. Source code can include these
1004 header files which automatically take care of the conditional #includes that
1005 the ``configure`` script generates.
1010 Most source files are here. By putting code in libraries, LLVM makes it easy to
1011 share code among the `tools`_.
1015 Core LLVM source files that implement core classes like Instruction and
1018 ``llvm/lib/AsmParser/``
1020 Source code for the LLVM assembly language parser library.
1022 ``llvm/lib/Bitcode/``
1024 Code for reading and writing bitcode.
1026 ``llvm/lib/Analysis/``
1028 A variety of program analyses, such as Call Graphs, Induction Variables,
1029 Natural Loop Identification, etc.
1031 ``llvm/lib/Transforms/``
1033 IR-to-IR program transformations, such as Aggressive Dead Code Elimination,
1034 Sparse Conditional Constant Propagation, Inlining, Loop Invariant Code Motion,
1035 Dead Global Elimination, and many others.
1037 ``llvm/lib/Target/``
1039 Files describing target architectures for code generation. For example,
1040 ``llvm/lib/Target/X86`` holds the X86 machine description.
1042 ``llvm/lib/CodeGen/``
1044 The major parts of the code generator: Instruction Selector, Instruction
1045 Scheduling, and Register Allocation.
1049 (FIXME: T.B.D.) ....?
1051 ``llvm/lib/ExecutionEngine/``
1053 Libraries for directly executing bitcode at runtime in interpreted and
1054 JIT-compiled scenarios.
1056 ``llvm/lib/Support/``
1058 Source code that corresponding to the header files in ``llvm/include/ADT/``
1059 and ``llvm/include/Support/``.
1064 Projects not strictly part of LLVM but shipped with LLVM. This is also the
1065 directory for creating your own LLVM-based projects which leverage the LLVM
1071 Feature and regression tests and other sanity checks on LLVM infrastructure. These
1072 are intended to run quickly and cover a lot of territory without being exhaustive.
1077 A comprehensive correctness, performance, and benchmarking test suite for LLVM.
1078 Comes in a separate Subversion module because not every LLVM user is interested
1079 in such a comprehensive suite. For details see the :doc:`Testing Guide
1080 <TestingGuide>` document.
1087 Executables built out of the libraries
1088 above, which form the main part of the user interface. You can always get help
1089 for a tool by typing ``tool_name -help``. The following is a brief introduction
1090 to the most important tools. More detailed information is in
1091 the `Command Guide <CommandGuide/index.html>`_.
1095 ``bugpoint`` is used to debug optimization passes or code generation backends
1096 by narrowing down the given test case to the minimum number of passes and/or
1097 instructions that still cause a problem, whether it is a crash or
1098 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1103 The archiver produces an archive containing the given LLVM bitcode files,
1104 optionally with an index for faster lookup.
1108 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1112 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1116 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1121 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1122 (although very slowly...). For architectures that support it (currently x86,
1123 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1124 compiler (if the functionality was compiled in), and will execute the code
1125 *much* faster than the interpreter.
1129 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1130 native code assembly file or to C code (with the ``-march=c`` option).
1134 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1135 (which are specified on the command line), and outputs the resultant
1136 bitcode. '``opt -help``' is a good way to get a list of the
1137 program transformations available in LLVM.
1139 ``opt`` can also run a specific analysis on an input LLVM bitcode
1140 file and print the results. Primarily useful for debugging
1141 analyses, or familiarizing yourself with what an analysis does.
1146 Utilities for working with LLVM source code; some are part of the build process
1147 because they are code generators for parts of the infrastructure.
1152 ``codegen-diff`` finds differences between code that LLC
1153 generates and code that LLI generates. This is useful if you are
1154 debugging one of them, assuming that the other generates correct output. For
1155 the full user manual, run ```perldoc codegen-diff'``.
1159 Emacs and XEmacs syntax highlighting for LLVM assembly files and TableGen
1160 description files. See the ``README`` for information on using them.
1164 Finds and outputs all non-generated source files,
1165 useful if one wishes to do a lot of development across directories
1166 and does not want to find each file. One way to use it is to run,
1167 for example: ``xemacs `utils/getsources.sh``` from the top of the LLVM source
1172 Performs an ``egrep -H -n`` on each source file in LLVM and
1173 passes to it a regular expression provided on ``llvmgrep``'s command
1174 line. This is an efficient way of searching the source base for a
1175 particular regular expression.
1179 Compiles all files in the current directory, then
1180 compiles and links the tool that is the first argument. For example, assuming
1181 you are in ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1182 path, running ``makellvm llc`` will make a build of the current
1183 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1188 Contains the tool used to generate register
1189 descriptions, instruction set descriptions, and even assemblers from common
1190 TableGen description files.
1194 vim syntax-highlighting for LLVM assembly files
1195 and TableGen description files. See the ``README`` for how to use them.
1199 An Example Using the LLVM Tool Chain
1200 ====================================
1202 This section gives an example of using LLVM with the Clang front end.
1207 #. First, create a simple C file, name it 'hello.c':
1214 printf("hello world\n");
1218 #. Next, compile the C file into a native executable:
1220 .. code-block:: console
1222 % clang hello.c -o hello
1226 Clang works just like GCC by default. The standard -S and -c arguments
1227 work as usual (producing a native .s or .o file, respectively).
1229 #. Next, compile the C file into an LLVM bitcode file:
1231 .. code-block:: console
1233 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1235 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1236 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1237 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1239 #. Run the program in both forms. To run the program, use:
1241 .. code-block:: console
1247 .. code-block:: console
1251 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1252 <CommandGuide/lli>`.
1254 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1256 .. code-block:: console
1258 % llvm-dis < hello.bc | less
1260 #. Compile the program to native assembly using the LLC code generator:
1262 .. code-block:: console
1264 % llc hello.bc -o hello.s
1266 #. Assemble the native assembly language file into a program:
1268 .. code-block:: console
1270 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1272 % gcc hello.s -o hello.native # On others
1274 #. Execute the native code program:
1276 .. code-block:: console
1280 Note that using clang to compile directly to native code (i.e. when the
1281 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1286 If you are having problems building or using LLVM, or if you have any other
1287 general questions about LLVM, please consult the `Frequently Asked
1288 Questions <FAQ.html>`_ page.
1295 This document is just an **introduction** on how to use LLVM to do some simple
1296 things... there are many more interesting and complicated things that you can do
1297 that aren't documented here (but we'll gladly accept a patch if you want to
1298 write something up!). For more information about LLVM, check out:
1300 * `LLVM Homepage <http://llvm.org/>`_
1301 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1302 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_